<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .parent{
            width: 200px;
            height: 200px;
            background-color: red;
            position: relative;
        }
        .child{
            width: 100px;
            height: 100px;
            background-color: gold;
            position: absolute;
            /* right: 50%;
            top:50%; */
            left: 0;
            bottom: 0;
        }
        body{
            height: 1000px;
        }
        .nav{
            width: 30px;
            height: 30px;
            background-color: hotpink;
            position: fixed;
            right: 10px;
            bottom: 50px;
        }
    </style>
</head>
<body>
    <div class="parent">
        <div class="child">

        </div>
    </div>

    <div class="nav"></div>
</body>
</html>